1. Field of the Invention
The present invention relates to a diagnosis unit for a copying apparatus or a printing apparatus.
2. Description of the Prior Art
In a prior art copying apparatus which carries out corona charging, exposure, development, corona transfer and residual image removal while a photosensitive drum is rotating, a corona charger and a discharger are turned on simultaneously with the start of rotation of the photosensitive drum.
In such an apparatus, if the photosensitive drum does not rotate in spite of a start of copy instruction by some reason, a local ununiform charge which is hard to remove is applied to the photosensitive drum by a high voltage of the corona charger activated by the instruction and the photosensitive drum may be deteriorated thereby.
In another prior art copying apparatus, a lamp is lit simultaneously with or immediately after document scan. In such an apparatus, if the document scan does not start in spite of a copy instruction, a document platen glass is heated by the lamp lit by the instruction and the document platen glass may be broken.
In other prior art copying apparatus which carries out latent image formation, development, transfer, residual image removal and jam detection while the photosensitive drum is rotating, a series of pulses are generated as the photosensitive drum is rotated and the pulses are counted to control various timings.
In such an apparatus, if the pulses are abnormal, timing error is produced and this error is detected to cut off a power supply of the apparatus.
However, if the power supply is cut off non-disriminately, a toner image may remain on the photosensitive drum, a high potential charge may remain or a transfer paper being separated may remain. As a result, various inconveniences are encountered in a first cycle after resumption of copying operation.
In the copying apparatus, when an image exposing lamp fails, no image is formed on a transfer paper and a sheet ejected has a solid black image thereon. If an operator continues copying operation in a multi-copy mode without noticing the failure, developer is wasted and a cleaner and a fixer are overloaded. In order to prevent such inconveniences, means for detecting the break of the lamp is provided so that the copying operation is immediately stopped when the break is detected.
However, the transfer paper remains unfed in the apparatus and it jams when the copying operation is resumed.
To avoid such a problem, it has been proposed not to stop the paper feed upon detection of the break of the lamp but to stop the feed of subsequent papers to prevent continuous paper feed.
In this case, however, the fed transfer paper has a solid black image thereon and the cleaner and the fixer are overloaded.